This 4-year study will enroll 750 HIV infected women and 250 HIV uninfected women who are participating in the WIHS study. Participants will undergo an initial ultrasound imaging of the neck to measure the size and thickness of the arteries. They will return for a repeat ultrasound at Years 2, 3, and 4 to assess any progression of atherosclerosis. Data from the participants’ biannual WIHS study visits, including HIV medication usage, viral load and CD4 test results, and occurrence of AIDS and other illnesses, will be reviewed. Results of participant’s inflammation marker tests, which may indicate the presence of atherosclerosis, including white blood cell count, C-reactive protein, E-selectin, and intercellular adhesion molecule 1, will also be reviewed.